The present invention relates to a reinforced flexible tubular pipe comprising an inner liner that forms a barrier against outflow of the medium that flows through the tubular pipe, said inner liner being encased by at least one reinforcing layer containing a number of profiles that have been coiled around the inner liner in such a manner that the profiles are entirely or partially contained in a lumen that allows transport of fluids in the longitudinal direction of the tubular pipe, and whereinxe2x80x94outside the reinforcing layerxe2x80x94an outer jacket is provided with a view to forming a barrier against unimpeded inflow of fluids and/or gases from the environment surrounding the tubular pipe and to the reinforcing layer. Such a reinforced flexible tubular is disclosed in Schlimmelpfennig, xe2x80x9cA novel flexible offshore LNG-pipe system with continues operating controlxe2x80x9d.
The reinforcing layer is not secured to the inner liner, but is able to move relative thereto which ensures the flexibility of the tubular pipe. Outside the reinforcing layer, an outer coating is provided with a view to forming a barrier against inflow of fluids and/or gasses from the environment surrounding the tubular pipe to the reinforcing layer.
However, positioning of reinforcing elements in the outer coating makes it possible to impart to this layer a structural functionality, too. Also, outside the outer jacket, a further reinforcing layer can be provided. To prevent collapse of the inner liner, it is often lined with a flexible steel pipe. In the following this pipe is designated xe2x80x98carcassxe2x80x99.
Most often such tubular pipes are used to transport fluids and gases at various depths of sea, and they are used in particular in situations where very high or varying water pressures prevail along the longitudinal axis of the pipe. Examples of such include riser pipes that extend from the seabed and up to an installation on or near sea level. In the technical literature this type of riser pipes is known as risers. Also between installations arranged on the seabed at great depth, or between installations near the surface of the sea, this type of tubular design is employed. Pipes for this use, are known in the technical literature as flowlines or jumpers.
The coiled reinforcing layer of the tubular pipe is configured of a number of layers of profiles, often of steel, mounted at like or different pitches.
During manufacture, transport and operation the tubular pipe is exposed to circumferential pressure as well as forces acting along the axis of the tubular pipe. It is thus the task of the reinforcing layer to absorb these forces to prevent the inner liner from being destroyed.
The specific configuration of the reinforcing layer depends on the use of the tubular pipe. It should be noted in particular in connection with the reinforcing layer that it contains a lumen between the coiled profiles which is necessary to enable the reinforcing profiles to move relative to each other. The movability of the reinforcing profiles is necessary to ensure the flexibility of the tubular pipe.
It is a problem with the known tubular pipes that a certain diffusion will always occur through the inner liner which means that undesired amounts of gases and condensate will accumulate in the reinforcing layer ia with ensuing. corrosion of the reinforcing profiles.
Furthermore accumulation of pressure in the reinforcing layer due to gas diffusion can cause the outer jacket to burst which will destroy the tubular member.
Several methods are known for reducing or preventing the destructive effect of diffusion into the reinforcing layer.
NO 300471 B1 discloses a method of ventilating the reinforcing layer towards the surroundings which is possible when a positive, super-atmospheric pressure prevails between the reinforcing layer and the surroundings.
A similar method is also described in U.S. Pat. No 4932810. However, it should be noted that the tubular pipe described in the US disclosure is of a different type.
WO 98/40657 A1 teaches how it is possible to construct a tubular member of two concentric shells so as to provide therebetween a flushing space. The flushing space thus accomplished is cleaned continually by a medium flowing therethrough.
Despite the fact that both NO 300471 B1 and WO 98/40657 A1 teach methods suitable for ventilating or cleaning reinforcing layers, both methods are less suitable for the maintenance of a flexible tubular member, the object of which being to transport fluids at great varying depths of sea.
The unsuitability of the methods is due to the fact that pipes operating at varying depths of sea are often attacked by gases and fluids that penetrate the reinforcing layer with ensuing formation of condensate, said condensate accumulating at the lowermost part of the pipe. NO 300471 B1 does not teach a method of removing such condensate, the valves shown in the patent for ventilation acting exclusively on gases that are ventilated at a positive difference of pressure between the reinforcing layer and the environment surrounding the tubular pipe.
Nor does WO 98/40657 A1 teach a method suitable for removal of condensates from the reinforcing layer on tubular pipes arranged below water at varying depths.
This is due to the fact that tubular pipes of the kind disclosed therein often contain a mixture of condensate and accumulated gases with an effective density which is substantially lower than that of water.
A forced flushing of the tubular pipe will therefore not be possible without pressurising the reinforcing layer near the point of entry for the flushing agent to a pressure that exceeds the ambient pressure. Pressurisation of the reinforcing layer, may entail a rupture of the outer jacket of the tubular pipe with ensuing destruction of the tubular pipe, bearing in mind that pressurisation of the tubular pipe with the object of flushing same can only be accomplished in practice provided the pressurisation occurs in the upper part of the tubular pipe.
In the light of this it is the object of the present invention to provide a reinforced, flexible tubular pipe that completely or partially remedies the above-mentioned drawbacks associated with the prior art pipes.
In accordance with the present invention this is accomplished by a tubular pipe of the type described in the introductory part which is characterised in that at least one flow path is arranged for conveying fluids from said lumen to the fluid transported in the inner liner of the tubular pipe.
In this manner it is possible, at all depths of sea, to empty the reinforcing layer without substantial, adverse pressurisation. Further advantageously, the surrounding environment is not exposed to contamination by fluids that derive from the reinforcing layers.
In some cases, eg in case of transport of aggressive fluids, the conditions of operation can be such that the flow path is advantageously, and as featured in claim 2, configured with means that prevent flow into the lumen of the fluid which is transported in the pipe interior.
Convenient embodiments of these means can be configured such, as featured in claim 3, that the means consist of a valve that allows flow only in case there is a negative difference in pressure between the pipe interior and the lumen.
In case the pressure within the pipe only rarely drops below the pressure in the reinforcing layers, the means can conveniently be configured in accordance with claim 4, ie in the form of a pump that forces the flow from the lumen and to the pipe interior, and furthermore the pump can, as featured in claim 5, be configured with a passageway or a bypass valve thereby enabling flow at any time provided there is a negative difference of pressure between the pipe interior and the lumen.
In this context it should be noted that use of a pump is particularly advantageous, the partial pressure (which is desirably low-value) of eg aggressive fluids in the free volume being hereby controllable, irrespective of the pressure within the inner liner of the pipe.
In an alternative embodiment there is, as featured in claim 6, provided a safety valve in the flow path. This safety valve can be used to optionally close the flow path completely to flow of fluid or gas, if desired.
Conveniently, as featured in claim 7, two or more blocking valves are provided that are, flow-wise, arranged on each their side of the means arranged in the flow path. Hereby the advantage is obtained that in case defaults occur in the valve or pump configured in the flow path with ensuing operational shutdowns, such failure can be remedied without resulting exposure of neither the lumen nor the pipe interior to the surroundings.
Moreover, the reinforced flexible tubular pipe can conveniently, and as featured in claim 8, comprise a coupling element for attachment of the reinforced flexible tubular member on another construction or to another tubular pipe where the flow path extends completely or partially into the coupling element.
In this manner, it can be completely or partially avoided to perforate the liner and the coating and optionally the reinforcing layer itself.
Moreover, in practice the reinforced flexible tubular pipe can, as described more detailed in claim 9, comprise at least two reinforced flexible tubular pipes, said tubular pipes being connected in extension of each other by means of connecting elements, and wherein the connecting element is provided with passages that allow fluid and gas in the one reinforced flexible tubular member to flow through the coupling element to the reinforcing layer in the second of the two reinforced flexible tubular pipes.
A further, preferred embodiment of the reinforced, flexible tubular pipe is, as featured in claim 10, additionally provided with at least one further flow path with a view to introducing to the reinforcing layer fluids or gases for cleaning and maintenance. Such cleaning fluids can be of a nature that prevents attacks on the reinforcement.
The present invention is particularly advantageous in connection with pipe installations in which the reinforced flexible tubular pipe is, as featured in claim 11, the cleaning and maintaining fluid or gas supplied to the lumen has a density comprised within the range of from 0.9 and 1.1 times the density of the sea water in which the pipe is used.
Moreover, the reinforced flexible tubular pipe is conveniently constructed in accordance with the features of claim 14 in that it comprises a plurality of reinforced flexible tubular pipes that extend between an installation arranged on the seabed and to a surface vessel or a platform at sea level.
Finally, claims 12 and 13 feature further convenient embodiments of the invention.